1. Field of the Invention
The present invention relates to a negative active material for a rechargeable lithium battery and a rechargeable lithium battery including the negative active material. More particularly, the present invention relates to a negative active material having a high capacity and excellent cycle-life characteristics for a rechargeable lithium battery and a rechargeable lithium battery including the negative active material.
2. Description of the Related Art
Rechargeable lithium batteries use materials capable of reversibly intercalating or deintercalating lithium ions in positive and negative electrodes, and include an organic electrolyte solution or a polymer electrolyte between the positive and negative electrodes. Rechargeable lithium batteries generate electrical energy by an oxidation/reduction reaction during the intercalation/deintercalation of lithium ions at the positive and negative electrodes.
For a positive active material, composite metal oxides, such as LiCoO2, LiMn2O4, LiNiO2, LiNi1-xCoxO2 (0<x<1), LiMnO2, and so on, have been researched.
Conventionally, lithium metals have been used as a negative active material for the rechargeable lithium battery. However, an explosion can be caused by a short circuit of the battery due to formation of dendrites when using the lithium metal. Therefore, carbonaceous materials, such as amorphous carbon, crystalline carbon, etc., have recently been used as the negative active material in place of lithium metals. However, such carbonaceous material imparts a non-reversible capacity of 5 to 30% during the first several cycles, which wastes lithium ions and prevents at least one active material from being fully charged and discharged. Therefore, it has a reduced energy density.
In addition, it has recently become known that a metal negative active material, such as Si, Sn, and so on, which is supposed to have a high capacity, has a problem in that it imparts non-reversible capacity characteristics. Furthermore, a tin oxide disclosed by Japan Fuji Film. Co., Ltd. has come into the spotlight as an alternative to the carbonaceous negative active material. However, since the metal negative active material is included at 30% or less, the initial Coulomb efficiency is decreased. Furthermore, since lithium is continuously intercalated and deintercalated to generate a lithium-metal alloy, the capacity is significantly decreased and the capacity preserving rate is substantially deteriorated after repeating 150 charge and discharge cycles so that it is not commercially viable. Accordingly, considerable research has been recently undertaken to improve these characteristics.